Second Age

When Sauron returned after escaping Númenor's destruction, he attacked the exiles of Númenor, and his forces took Minas Ithil by storm.
When the Last Alliance of Elves and Men defeated Sauron in the year 3429 of the Second Age, Minas Ithil was restored as a watchtower.

Third Age

In the year 1980 of the Third Age, the Nazgûl returned to Mordor (after the defeat of the Witch-king of Angmar in the north of Middle-earth).
The Ringwraiths laid siege to Minas Ithil shortly after their return, in 2002, and they took the city for their master, Sauron (who was still hidden at the time).
Minas Ithil was occupied by fell creatures, and it changed into a foul, evil place. As a result, it came to be called Minas Morgul, which in the tongue of Gondor means "The Tower of Dark Sorcery".

Following the events of The Lord of the Rings, the bridge leading to Morgul Vale was pulled down by the Army of the West and its fields set aflame, and they met no opposition as the entire city's garrison had been killed at the Battle of Pelennor Fields. Minas Morgul abandoned and fell into decay as it had become too foul for human habitation. After the War of the Ring, Faramir was made Prince of Ithilien by King Elessar, who advised him to make his abode in the Emyn Arnen southeast of Minas Tirith. Faramir ruled from there with his new bride Éowyn, for King Elessar counseled that even though Minas Morgul was completely abandoned, the land was such a terror on the minds of Men that it would not be fit for habitation or even human contact for many years. Eventually, the city was rebuilt as Minas Ithil and the evil that tainted the land was at last gone.

In fashion Minas Morgul seems to have been much like Minas Ithil, except for the replacement of beauty by terror. The top most course of the tower revolved slowly, and the walls of Morgul shone with a pale, frightening light.